POLYCENTRIC MULTI-PHASE DECCAN VOLCANISM: IS CAUSATIVE LINKAGE TO K-PG BOUNDARY VALID?

Reassessment of the geochronological, paleomagnetic and volcanological data from the Deccan Volcanic Province (DVP) indicates a hitherto unrecognised zonation of its eruptive history. Each of these sub-provinces appear to have an (interlinked, but) independent eruptive history.

The thickest pile in the western part (that hosts the best studied sequence) was emplaced in 3 phases with the oldest (and apparently the most voluminous) centred around 67.5+0.5 Ma, followed by another between 63 – 64 Ma (focused south of the earlier ones), and a late phase that continued well beyond 62 Ma along the western coastal tract. The earliest Deccan lavas (~ 68 Ma) are preserved in the Malwa region, fed by eruptive centres along the Narmada and Tapi valleys that may have remained active longer, as indicated by the NRN magnetic sequence (=? C30N – C29R – C29N) preserved in them. The early eruptions in the north-western DVP (Kutch) have ages comparable to the early eruptions in the western DVP. Interestingly, ages of eastern lavas from the Madla (Amarkantak) lobe are younger that the K-Pg boundary by almost a million years, with an imprint of a NRN magnetic sequence. This does not justify their temporal equivalence with the west DVP sequence. Models based on long-distance correlation of chemical types from the Western DVP with the other parts are ambiguous, unless the active duration of overland movement of such flows is accepted to be of the order of a million years, an assumption not borne out by the physical volcanological nature of the Deccan lavas.

Physical volcanological data of lava sequences across the province shows that the Deccan volcanism is more aptly modelled analogous to the Icelandic type continental fissure-type eruptions rather than the Hawaiian monocentric eruptions. The intensity and magnitude of environmental crisis resulting from the Deccan volcanism –although severe – is revisited in light of the emerging data on its stratigraphic classifications, age and duration. A combination of terrigenous volcanism setting the tone for the environment crisis coupled with extra-terrestrial (Chicxulub and associated meteoritic shower) impacts may be more appropriate to explain the dramatic events of extinction and biotic turn-over that occurred across the K-Pg boundary.